For example, Patent Document 1 discloses an electronic component (microphone package) in which the semiconductor element is mounted on the printed substrate while covered with a cap. In the electronic component disclosed in Patent Document 1, as illustrated in modes of FIGS. 1 to 3, a microphone 11 produced by utilizing a MEMS technology has a cavity 12 in a central portion of a lower surface thereof, and the lower surface of the microphone 11 is die-bonded to an upper surface of a printed substrate 14 using an epoxy resin 13. During the die bonding of the microphone 11 to the printed substrate 14, when the epoxy resin 13 held down by the microphone 11 flows in the cavity 12, a volume of the cavity 12 varies due to the flowing-in resin, or a thickness of the epoxy resin 13 between the microphone 11 and the printed substrate 14 varies due to flow-out of the epoxy resin 13, whereby possibly a characteristic of the microphone 11 is adversely affected. Therefore, in Patent Document 1, a retaining ring 15 is provided in the upper surface of the printed substrate 14 in the cavity 12 to prevent the die bonding epoxy resin 13 from flowing in the cavity 12, thereby suppressing the adverse affect on the microphone 11.
Specifically, in the mode of FIG. 1, a lower-surface inner peripheral portion of the microphone 11 overlaps retaining ring 15, and a lower-surface outer peripheral portion of the microphone 11 and the printed substrate 14 are bonded by the epoxy resin 13. Therefore, during the die bonding of the microphone 11 with the epoxy resin 13, the retaining ring 15 prevents the epoxy resin 13 from flowing into the cavity 12.
However, in the mode of FIG. 1, because there is no consideration for the epoxy resin 13 flowing to the outside of the microphone 11, the epoxy resin 13 flowing to the outside cannot be suppressed. Therefore, the epoxy resin 13 flows to the outside until the epoxy resin 13 is cured by heat, occasionally the flowing-out epoxy resin 13 reaches a ground pattern 17 that connects a metallic cap 16 to a ground potential. The metallic cap 16 is bonded to the ground pattern 17 by a conductive bonding resin in order that the metallic cap 16 and the printed substrate 14 constitute a Faraday cage to shield external high-frequency noises. When the flowing-out epoxy resin 13 forms a nonconductive coating in a surface of the ground pattern 17 before the metallic cap 16 is bonded, an electric conduction defect is generated between the metallic cap 16 and the ground pattern 17 at that point, and a high-frequency noise shielding property is degraded.
Conventionally, a sufficient distance may be provided between the ground pattern 17 and a region where the microphone 11 is die-bonded. However, when the distance is increased, eventually a footprint of the electronic component is enlarged, and a size of the electronic component is enlarged to prevent the miniaturization of the electronic component.
In the mode of FIG. 2, the whole lower surface of the microphone 11 is bonded to the printed substrate 14 by the epoxy resin 13, the retaining ring 15 is provided in the cavity 12 to block the epoxy resin 13 flowing into the cavity 12.
In the mode of FIG. 3, the thickness of the retaining ring 15 is increased in order to enhance the effect that the retaining ring 15 blocks the epoxy resin 13 in the mode of FIG. 2.
However, in the modes of FIGS. 2 and 3, even if an application amount of the epoxy resin 13 is correctly managed, or even if a pressing force of the microphone 11 is managed so as to be kept constant, the amount of epoxy resin 13 flowing out from the lower surface of the microphone 11 varies depending on the time the applied epoxy resin 13 is cured or a temperature of an external environment, a variation in resin thickness between the lower surface of the microphone 11 and the printed substrate 14 is increased after the curing. As a result, an elastic property changes due to the variation in volume of the cavity 12 or the variation in thickness of the epoxy resin 13, and the characteristic of the microphone 11 may be affected.
Conventionally, the external environment may be strictly managed in an assembly process, and process management is strictly performed such that the time to perform resin baking (a process for curing the epoxy resin 13 by heating) since the epoxy resin 13 is applied is shortened. However, from the viewpoint of cost, undesirably expensive environmental facilities are required in order to strictly manage the external environment in the assembly process. When the time to perform the resin baking since the epoxy resin 13 is applied is shortened, it is necessary to diligently put the electronic component in a baking furnace. Therefore, temperature management of the baking furnace becomes difficult while labor cost is increased, which results in undesirable cost increase.
Further, in the mode of FIG. 2, because the retaining ring 15 is formed by a conductor pattern of the printed substrate 14, the microphone 11 is fixed by the epoxy resin 13 to the region where the conductor pattern of the printed substrate 14 is removed. Because the conductor pattern of the printed substrate 14 functions to shield the external high-frequency noise along with the metallic cap, the high-frequency noise shielding property is degraded immediately below the microphone 11 in the mode of FIG. 2. At the same time, because the conductor pattern of the printed substrate 14 largely contributes to whole rigidity of the electronic component, the rigidity of the electronic component is degraded by removing the conductor pattern in the region, which possibly generates the adverse affect on the function of the electronic component.
On the other hand, in the mode of FIG. 3, in order to provide the retaining ring 15 having the large thickness, it is necessary that the retaining ring 15 be formed by adding another member different from the conductor pattern of the printed substrate 14, which unfortunately results in the cost increase.
Patent Document 1: U.S. Pat. No. 7,166,910